1. Field of the Invention
The present invention relates to polycyclic iminooxadiazinediones prepared from 1,4-diisocyanates, to a process for their production and to their use for the production of polyisocyanate addition products.
2. Description of the Prior Art
The reaction of isocyanates with an exceptionally large number of H-acid compounds to synthesize high molecular weight polymers based on the work of O. Bayer et al. is known (for example, DE-A 728,981) and has found substantial industrial application. Use is made of the high reactivity of the isocyanate groups with the co-reactants.
The unpleasant physiological properties of low-molecular isocyanates, in particular diisocyanates, occasionally prevent their direct use, for example, in the coatings sector. Various methods are therefore employed for the modification of these monomers with the aim of considerably increasing the vapor pressure of the resulting products and obtaining physiologically safe compounds. Examples of this are the reaction of excess quantities of diisocyanates with dihydric and polyhydric alcohols to form prepolymers as well as the preparation of polyisocyanates saving uretdione ("dimer"), isocyanurate ("trimer") and biuret groups.
In addition, it is occasionally necessary to use NCO groups having reduced reactivity, e.g., in one-component applications with as long a pot life as possible, polyurethane powder coating systems and aqueous systems. To obtain products which can be employed in these applications, it is necessary to carry out a thermally or chemically reversible blocking reaction using compounds, which are split off, optionally in altered form, during the cross-linking reaction to form the polymeric synthetic material or coating film (for example, Progr. Org. Coatings, 3 (1975), 73 and 9 (1981), 3). A number of compounds have proven to be successful in practice for this purpose, for example, .di-elect cons.-caprolactam, dialkyl malonate esters and butanone oxime.
The disadvantage of all these systems is that the blocking agents, which are split off during the curing reaction, have to be disposed of. Otherwise, if they remain in the products, they can adversely affect their range of properties, for example, due to "exudation" or to a deterioration in the physical and/or chemical stability of the products.
In some respects an exception to this disadvantage are the above-mentioned coating polyisocyanates containing uretdione groups ("dimers"), which, in contrast to the many other isocyanate derivatives, may be thermally split into the original isocyanates. Therefore, no decomposition product is released during the curing process.
However, several disadvantages may result from the thermal lability of the uretdione structure. Prolonged storage at an elevated temperature may lead to a slow splitting of the uretdione rings, which results in an increase in the content of residual monomers and consequently in products which are no longer physiologically unobjectionable. Also, the thermally induced dissociation of the uretdione rings, which is necessary for the rapid curing of the composition, takes place only at relatively elevated temperatures, which may lead to discoloration and other unwanted decomposition phenomena.
Also known is the use of the "self-blocking" compounds of the so-called .alpha.-nylon type, which are described in EP-A 14,365 and are similar to uretdiones. However, the splitting of these polymers, which is necessary for the cross-linking, succeeds if at all only at higher temperatures than the temperatures needed for uretdiones. For this reason they have not been previously used, in particular in the coatings sector.
An object of the present invention is to develop systems wherein none or at least a distinctly decreased amount of the isocyanate groups, when compared to known prior art systems containing blocking agents, have to be deactivated by the addition of a blocking agent and nevertheless, even at elevated temperature, do not split into monomeric diisocyanates.
This object may be achieved with the bicyclic and polycyclic iminooxadiazinediones (hereinafter polycyclic iminooxadiazinediones) according to the invention.